The present invention relates generally to a method of treating red mud, to permit it more readily to be put to further uses.
Red mud is a waste product which is produced in the manufacture of aluminium. The starting material bauxite which includes inter alia iron and aluminium oxide is digested with caustic soda or soda at elevated temperatures. In the course of the process, aluminium is dissolved, while iron oxide (Fe.sub.2 O.sub.3 ;Fe.sub.3 O.sub.4) and other solid materials present remain in finely divided form in an alkaline aqueous suspension. The suspension is then filtered at temperatures of about 70.degree. C., for example on a drum-type filter. In that operation, the red mud is deposited on the drum filter cloth, from which it is stripped or scraped off. Generally, the arrangement is such that the red mud then drops into a collecting channel which is disposed under the drum filter and which is flushed through with water so that the red mud undergoes further dilution and can be conveyed to a waste dump by way of a pipeline. This means that the red mud is normally treated as a waste product. However, there is also a restricted number of uses to which red mud can be put, for example as a catalyst in the hydrogenation of coal, a process that requires the presence of a catalyst for accelerating the hydrogenating reaction. However, the use of red mud has hitherto been subject to certain limitations, which is essentially to be attributed to the fact that it is very difficult to handle. That is because on the one hand, red mud represents an oily dirty product, and also in particular depending on the conditions of transportation and handling, there may be the danger of further compacting of the solid substance therein, more specifically also in the sense of partial separation of the solid phase from the liquid phase, with the result that an alkaline aqueous phase is separated off. That requires particular measures to be taken in order to safeguard it, for example to prevent it from uncontrolledly running out or leaking for example from a transportation container or the like. Consequently, a procedure which has been adopted is that of drying the red mud before it is put to further use.
Red mud usually has a water content of between 40 and 60%, which can be removed by the application of heat, but such a drying process requires additional and generally complicated equipment, and also involves the consumption of a large amount of energy.